The origin of this fundamental "crustal dichotomy" is uncertain both in terms of how and when it formed. But this recent discovery of the numerous buried craters may pin down the answer to when the lowlands first formed.

Boulder - Nov 8, 2001Soon after Mars was formed, it was bombarded by numerous large meteorites and asteroids. Scientists have discovered an unexpectedly large grouping of impact basins buried under Mars' northern plains that resulted from this pounding. They used Mars Orbiter Laser Altimeter (MOLA) topographic data to find them, because they can't be seen in images of the Martian surface.

Above these basins are thin young plains, but the lowland crust beneath them is actually extremely old and was formed very, very early. According to Herbert Frey of the Geodynamics Branch of NASA's Goddard Space Flight Center, this is a radical departure from the popular belief that the northern lowlands were formed later in Martian history, perhaps by plate tectonic style processes.

Frey discussed these findings November 8, at the Geological Society of America's annual meeting in Boston, Massachusetts.

This discovery is a crucial piece to one of the greatest unsolved puzzles about Mars-why does its surface have two distinct hemispheres: one that is high and heavily cratered and one that is low and sparsely cratered?

The origin of this fundamental "crustal dichotomy" is uncertain both in terms of how and when it formed. But this recent discovery of the numerous buried craters may pin down the answer to when the lowlands first formed.

"The ancient age of the lowlands means whatever process produced them occurred both early and relatively quickly," explained Frey. "Things like plate tectonics may not work.

"Another ramification is that there have been lowlands in the northern parts of Mars for essentially all of Martian history. That means that at whatever early time conditions permitted liquid water to exist on Mars, there was a northern lowland into which that water could drain.

"So it is quite possible that a shallow ocean may have existed on Mars very early in its history, as some have suggested based on completely different data."

"The origin of the crustal dichotomy on Mars has been one of the main areas of my own research for a long time, so anything that could tell us how old the lowlands really were naturally was of interest," Frey said.

"And of course, the discovery aspects of 'seeing' (in elevation data) things that no one else had ever seen or even guessed might be there is intrinsically intoxicating. Not only has this work turned out to be very important, but it's also been fun!"

Ancient, Gigantic Drainage Basin Became Aquifer On MarsTucson - Oct 9, 2001An enormous ancient drainage basin and aquifer system lies hidden and deformed in one of the most geologically dynamic landscapes on Mars, scientists conclude from a comprehensive, more than 10-year study.

Scientists Find Largest Flood Channels in the Solar SystemTucson - Aug 1, 2001Scientists may have discovered the largest flood channels in the solar system on Mars where a system of gigantic ancient valleys, some as much as 200 kilometers wide, lies partly buried under a veneer of volcanic lava flows, ash fall and wind-blown dust in Mars' western hemisphere.

Watery Tales From TexasCameron Park - May 4, 2001Some theorists at this year's Lunar and Planetary Sciece Conference again reiterated their belief that there is evidence that substantial amounts of liquid water flowed on at least some parts of Mars not just in its earliest times, but occasionally in much more recent geological times -- perhaps less than a hundred million years ago.

Tectonics Not Oceans Shaped Ancient RidgesTucson - April 4, 2001What scientists suspect might be ancient ocean shorelines on the northern plains of Mars is actually a network of tectonic ridges related to dramatic martian volcanism, a University of Arizona planetary sciences graduate student and a collaborating post-doctoral researcher at the Massachusetts Institute of Technology report in the April 5 issue of Nature.

Sedimentary Rocks Suggest An Ancient Land of Martian LakesWashington - Dec. 4 2000Layered geologic outcrops on Mars, that will be described in this week's issue of the journal Science -- may be composed of sedimentary rock that dates from the earliest span of martian history, between 4.3. and 3.5 billion years ago.

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